1. Field of Invention
This invention relates generally to electric motors and methods of operation therefor and, more specifically, to an efficient, reliable computer controlled electric motor and method of operation therefor.
2. Description of the Prior Art
Various types of electric motors have been developed, in the past, for different types of applications. One such electric motor is known as a stepper motor. A defining quality of the stepper motor is that a distinct quantum of rotation of a rotor occurs in response to an electrical input pulse. The discrete quantum is known as a step. Desirable features of the stepper motor include its not having either a commutator, brushes, slip rings or rotor windings.
Like most electric motors, the stepper motor is comprised of a rotor and a stator that are separated by an air gap. In one type of stepper motor, the rotor is a permanent magnet. The stator includes a plurality of stator coils. The electrical input pulse is applied to the stator coils.
When a train of electrical input pulses is applied, a rotating field is produced that causes continual rotation of the rotor. The continual rotation is conveniently thought of as sequential stepping. Another desirable feature of the stepper motor is that by controlling the application of the electrical input pulses, any of a multiplicity of desired rotor positions are achievable without the use of a feedback loop.
To produce the rotation, the electrical input pulse causes the stator coils to magnetize a portion of the stator that resembles teeth of a gear. The permanent magnet of the rotor also has a portion that resembles the teeth of the gear. When a stator tooth and a rotor tooth are proximal to each other and there is a slight angular displacement therebetween, a magnetic force of repulsion (or attraction) causes the rotor to rotate relative to the stator.
Although the stepper motor has several desirable features, it is not efficient and does not develop sufficient power for propelling a battery powered motor vehicle (i.e. electric car, a truck, etc.), for example.
Because a step occurs in response to the input electrical pulse, the rotor may not have a smooth, constant rotation suitable for rotating a workpiece in a lathe, for example. Accordingly, there is a need for an electric motor that is efficient, has a capability of producing sufficient power, can rotate a workpiece smoothly and has the desirable features of the stepper motor.